The invention pertains to a rotatable cutting tool that is useful for the impingement of earth strata such as, for example, asphaltic roadway material, coal deposits, mineral formations and the like. More specifically, the present invention pertains to a rotatable cutting tool that is useful for the impingement of earth strata, and especially a cutting tool body that is a component of such a rotatable cutting tool. The cutting tool body exhibits improved hardness properties to thereby provide improved performance characteristics (e.g., wear resistance and toughness) for the entire rotatable cutting tool.
Heretofore, rotatable cutting tools have been used to impinge earth strata such as, for example, asphaltic roadway material. U.S. Pat. No. 4,201,421 to Den Besten et al,. and U.S. Pat. No. 4,497,520 B2 to Ojanen are exemplary of rotatable cutting tools used to impinge earth strata, and especially asphaltic roadway material.
Generally speaking, rotatable cutting tools useful to impinge earth strata have an elongate cutting tool body typically made from steel and a hard tip (or insert) affixed to the cutting tool body at the axial forward end thereof. The hard tip is typically made from a hard material such as, for example, cemented (cobalt) tungsten carbide. The rotatable cutting tool is rotatably retained or held in the bore of a tool holder such as shown in U.S. Pat. No. 6,478,383 to Ojanen et al. In the alternative, the rotatable cutting tool is retained in the bore of a sleeve that is, in turn, held in the bore of a holder such a shown in U.S. Pat. No. 6,786,557 to Montgomery, Jr.
The holder is affixed to a driven member such as, for example, a driven drum of a road milling machine. In some designs, the driven member (e.g., road milling drum) carries hundreds of holders wherein each holder carries a rotatable cutting tool. Hence, the driven member may carry hundreds of rotatable cutting tools. The driven member is driven (e.g., rotated) in such a fashion so that the hard tip of each one of the rotatable cutting tools impinges or impacts the earth strata (e.g., asphaltic roadway material) thereby fracturing and breaking up the material into debris. U.S. Pat. No. 5,536,073 to Sulosky et al. is exemplary of a road milling drum.
As can be appreciated, rotatable cutting tools that impinge earth strata such as asphaltic roadway material operate in a severe environment. The severe operational environment subjects the components of the rotatable cutting tool to both severe abrasive wear and severe stress.
In order to provide an improved useful tool life, it would be desirable to provide a cutting tool body that would exhibit improved resistance to abrasive wear. A more wear-resistant cutting tool body would be better able to withstand severe wear conditions, and thereby would be less likely to experience premature failure due to premature (or excessive) wear.
In order to provide an improved useful tool life, it would be desirable to provide a cutting tool body that would exhibit improved toughness. A tougher cutting tool body would be better able to withstand severe operating conditions, and thereby would be less likely to experience premature failure (e.g., catastrophic stress fracturing) due to operational stress.
As one can appreciate, if a cutting tool body does not exhibit sufficient wear resistance and/or toughness, there exists the risk that the cutting tool body may prematurely fail. Such a premature failure of the cutting tool body is an undesirable result that typically leads to the termination of the useful life of the rotatable cutting tool, as well as a decrease in the operational efficiency of the road milling machine. Overall, it thus is apparent that it would be very desirable to provide an improved rotatable cutting tool that has an improved cutting tool body wherein the cutting tool body exhibits improved wear resistance and improved toughness.